Light emitting diode and method of manufacturing the same

ABSTRACT

A light emitting diode and a method of manufacturing the light emitting diode are provided. The light emitting diode includes an n-type semiconductor layer, an inclined type superlattice thin film layer, an active layer, and a p-type semiconductor layer. The n-type semiconductor layer is disposed on a substrate. The inclined type superlattice thin film layer is disposed on the n-type semiconductor layer and includes a plurality of thin film pairs in which InGaN thin films and GaN thin films are sequentially stacked. The active layer having a quantum well structure is disposed on the inclined type superlattice thin film layer. The p-type semiconductor layer is disposed on the active layer. Composition ratio of Indium (In) included in the InGaN thin film is increased as getting closer to the active layer. Thus, internal residual strain is reduced, and quantum confinement effect is enhanced, and internal quantum efficiency is increased.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0104731, filed on Jul. 24, 2015, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates to a light emitting diode, and morespecifically, to a light emitting diode including an inclined typesuperlattice thin film layer and a method of manufacturing the same.

2. Discussion of Related Art

A light emitting diode (LED) is a semiconductor light emitting unitformed by a bonding structure of an n-type semiconductor layer and ap-type semiconductor layer including compound semiconductor material.Generally, the light emitting diode is a kind of an optoelectronicdevice configured to emit energy corresponding to a band gap between aconduction band and a valance band in a form of light by recombinationof electrons from the n-type semiconductor layer and holes from thep-type semiconductor layer when a forward voltage is applied. Such alight emitting diode has advantages in terms of an excellent energyefficiency, color uniformity, long lifetime, or the like and thus maynot only be applied as a main light source of a head lamp of anautomobile, an illumination device, and a display, but also becomingbroadly applied in skin care and the medical area recently.

The light emitting diode is mainly manufactured of nitride-basedcompound semiconductor material of III-V group such as AlN, GaN, InN, orthe like. Since the nitride-based compound semiconductors have wide bandgaps in a range of about 0.7 eV to about 6.2 eV, various wavelengths arerealized by adjusting composition of the compound. Also, as a directtransition type semiconductor, the nitride-based compound semiconductorhas rapid response speed, high electron mobility, and high thermal andchemical stability, is capable of being operated at a high temperature,and thus, is widely used in the fields of optoelectronic device withhigh luminance and large output electric device.

Generally, in order to realize various wavelengths in the light emittingdiode, composition ratio of indium (In) in the nitride-based compound isvaried to control the wavelength, but when the composition ratio of theindium (In) is increased, indium (In) segregation phenomenon, internaldefects due to a lattice mismatch, or the like are generated, and thus,light output efficiency of the light emitting diode is rapidlydecreased. In particular, the above problem is more severe in a longwavelength (green wavelength), and the above phenomenon is referred toas a green gap.

Also, a strong compressive strain is generated by a large difference oflattice constant between InGaN and GaN, band-bending of energy isgenerated, recombination of carriers, that is, injected electrons andholes, is not made, and thus the carriers don't contribute to lightemission. Thus, efforts for an increase of light output efficiency andimprovement of internal quantum efficiency for the long wavelength areneeded.

Recently, in order to solve the above problem, a technology formanufacturing a green light emitting diode of large output using anonpolar or semipolar substrate and a technology for changing astructure of a quantum well to control defects and internal residualstrain are being developed, but the above green gap problem stillremains as a problem in manufacturing a high efficiency light emittingdiode.

SUMMARY

The present disclosure is directed to a light emitting diode capable ofreducing internal residual strain of a light emitting diode, decreasingdefects and enhancing confinement effect of carriers to increaseinternal quantum efficiency and a method of manufacturing the same.

According to an aspect of the present invention, there is provided alight emitting diode. The light emitting diode includes an n-typesemiconductor layer, an inclined type superlattice thin film layer, anactive layer, and a p-type semiconductor layer. The n-type semiconductorlayer is disposed on a substrate. The inclined type superlattice thinfilm layer is disposed on the n-type semiconductor layer, and includes aplurality of thin film pairs in which InGaN thin films and GaN thinfilms are sequentially stacked. The active layer having a quantum wellstructure is disposed on the inclined type superlattice thin film layer.The p-type semiconductor layer is disposed on the active layer.Composition ratio of Indium (In) included in the InGaN thin film isincreased as getting closer to the active layer. The inclined typesuperlattice thin film layer may have a structure in which the thin filmpairs of 2 to 100 are disposed.

The inclined type superlattice thin film layer may reduce band bendinggenerated by a lattice mismatch in the quantum well structure of theactive layer, and the n-type semiconductor layer and the p-typesemiconductor layer may include an n-type GaN layer and a p-type GaNlayer, respectively.

The light emitting diode may further include a GaN layer interposedbetween the inclined type superlattice thin film layer and the activelayer.

According to another aspect of the present invention, there is provideda method of manufacturing a light emitting diode. The method includesforming an n-type semiconductor layer on a substrate, forming aninclined type superlattice thin film layer including a plurality of thinfilm pairs in which InGaN thin films and GaN thin films are sequentiallystacked on the n-type semiconductor layer, forming an active layerhaving a quantum well structure on the inclined type superlattice thinfilm layer, and forming a p-type semiconductor layer on the activelayer. Composition ratio of Indium (In) included in the InGaN thin filmis increased as getting closer to the active layer.

Forming of the inclined type superlattice thin film layer may include afirst step of forming the InGaN thin film, and a second step of removingindium included in an upper portion of the InGaN thin film to form thethin film pairs in which the InGaN thin films and the GaN thin films aresequentially stacked. The first step and the second step may bealternately performed repeatedly in a plurality of times.

The first step may be performed under nitrogen atmosphere using a metalorganic chemical vapor deposition (MOCVD) method.

The second step may include supplying hydrogen (H₂) on an upper portionof the InGaN thin film and removing indium (In) included in the upperportion of the InGaN thin film, and the hydrogen may be supplied for 25seconds to 30 seconds at a speed in a range of 8,000 sccm to 8,500 sccm.

The inclined type superlattice thin film layer may be formed byalternating performing the first steps and the second steps repeatedly 2to 100 times, and after the first steps and the second steps arealternately performed, the steps may be performed at a temperature lowerthan the temperature of previous steps during the repeatedly performingthe first step and the second step. In particular, during repeatedlyperforming of the first step and the second step, the steps may beperformed at a temperature lower than the temperature of previous stepsby about 5° C.

Before forming of the active layer of the quantum well structure on theinclined type superlattice thin film layer, the method may furtherinclude forming a GaN layer on the inclined type superlattice thin filmlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other subjects, features, and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing in detail embodiments thereof with reference to theaccompanying drawings, in which:

FIGS. 1A to 1D are schematic diagrams illustrating a method ofmanufacturing a light emitting diode according to one embodiment of thepresent invention;

FIG. 2 is a schematic diagram illustrating a method of manufacturing aninclined type superlattice thin film layer according to one embodimentof the present invention;

FIGS. 3A and 3B are schematic diagrams illustrating a method ofmanufacturing a light emitting diode according to another embodiment ofthe present invention;

FIGS. 4A and 4B are a schematic diagram illustrating a structure of alight emitting diode according to one embodiment of the presentinvention and an image of a light emitting diode manufactured byEmbodiment 1 observed using a transmission electron microscope (TEM);

FIG. 5 is a table illustrating change of process temperature duringmanufacturing a light emitting diode according to Embodiment 1 andComparative Embodiments 1 to 3 of the present invention;

FIGS. 6A and 6B are tables illustrating photoluminescence intensity (PLintensity) according to a change of wavelength and temperature accordingto Embodiment 1 and Comparative Embodiments 1 to 3 of the presentinvention; and

FIGS. 7A and 7B are tables illustrating electrical characteristicsaccording to wavelength according to Embodiment 1 and ComparativeEmbodiments 1 to 3 of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail below with reference to the accompanying drawings.

The present invention is not limited to the embodiments and theaccompanying drawings disclosed and is only defined by the scope of theappended claims. Accordingly, it will be apparent to those skilled inthe art that various modifications, equivalents, and alternatives can bemade to the described embodiments of the present invention withoutdeparting from the spirit or scope of the invention, and it is intendedthat the present invention is to cover all such modifications,equivalents, and alternatives. The same reference numbers will be usedthroughout this specification to refer to the same or like components.

Method of Manufacturing Light Emitting Diode Including Inclined TypeSuperlattice Thin Film Layer

According to one aspect of the present invention, a method ofmanufacturing a light emitting diode is provided. In particular, themethod of manufacturing the light emitting diode includes 1) forming ann-type semiconductor layer on a substrate, 2) forming an inclined typesuperlattice thin film layer with a structure having a plurality of thinfilm pairs in which an InGaN thin film and a GaN thin film aresequentially stacked on the n-type semiconductor layer, 3) forming anactive layer of a quantum well structure on the inclined typesuperlattice thin film layer, and 4) forming a p-type semiconductorlayer on the active layer. Here, composition ratio of indium (In)included in the InGaN thin film may increase as getting closer to theactive layer.

FIGS. 1A to 1D are schematic diagrams illustrating a method ofmanufacturing a light emitting diode according to one embodiment of thepresent invention.

Referring to FIG. 1A, the method of manufacturing the light emittingdiode of the embodiment of the present invention may include 1) formingan n-type semiconductor layer 200 on a substrate 100.

The substrate 100 may have a predetermined light transmittance and maybe a material which may facilitate growing of the n-type semiconductorlayer 200. In particular, the substrate 100 may formed of at least onematerial selected from sapphire (Al₂O₃), Si, SiC, glass, quartz,ceramic, Ge, GaAs, GaP, InP, InAs, GaN, and AlN. For example, when thelight emitting diode includes a nitride-based compound semiconductor andhas a structure of a hexagonal lattice, the substrate 100 may be formedof a material also having a structure of a hexagonal lattice. In theembodiment of the present invention, the substrate 100 may be formed ofsapphire.

In the embodiment of the present invention, before the n-typesemiconductor layer 200 is formed on the substrate 100, a buffer layer(not shown) may be formed on the substrate 100. Generally, the bufferlayer is formed in order to reduce the lattice mismatch of a substrateand may be formed on the entire surface of the substrate. The bufferlayer may generally use any one material selected from SiC, ZnO, Si,GaAs, AlN, and GaN which are generally not doped by dopants but is notlimited by the above.

The n-type semiconductor layer 200 represents a semiconductor layerdoped with n-type dopants, and the n-type dopants may be silicon (Si).In particular, for example, the n-type semiconductor layer 200 mayinclude nitride-based compound semiconductor layer having any onematerial selected from GaN and Al_(x)Ga_((1-x))N(0≦x≦1). In theembodiment of the present invention, the n-type semiconductor layer 200may include an n-GaN layer.

The n-type semiconductor layer 200 may be formed on the substrate 100through methods of metal organic chemical vapor deposition (MOCVD),hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), e-beamdeposition, sputtering, or the like, but is not limited by the abovemethods.

Referring to FIG. 1B, the method of manufacturing the light emittingdiode of the embodiment of the present invention may include 2) forminga superlattice thin film layer 300 on the n-type semiconductor layer200. The inclined type superlattice thin film layer 300 may have astructure including a plurality of thin film pairs in which InGaN thinfilms 301 a, 302 a, . . . (300+n)a and GaN thin films 302 b, . . .(300+n)b are sequentially stacked. Unlike a conventional superlatticethin film layer, the inclined type superlattice thin film layer may havea sloped indium (In) concentration gradient in which composition ratioof indium (In) in the inclined type superlattice thin film layerincreases as getting closer to the active layer. The n represents thenumber of the thin film pairs and may be an integer in a range of 2 to100. The inclined type superlattice thin film layer according to theembodiment of the present invention and the effect thereof may berealized when the number of the thin film pairs is in the plural, thatis, more than one pair, thus the number of the thin film pairs must beat least two. Also, when the number of the thin film pairs is more than100, the total thickness of the inclined type superlattice thin filmlayer is too thick, and the distance that electrons injected into thelight emitting diode move may become large. That is, when the thicknessof the inclined type superlattice thin film layer is thick, resistancemay be increased and dispersion of electrons and loss caused by defectsmay occur, and thus, the number of the thin film pairs may be less than100. In the embodiment of the present invention, the n may be 12.

In particular, the formation of the inclined type superlattice thin filmlayer 300 includes a first step of forming the InGaN thin film and asecond step of removing indium (In) included in an upper portion of theInGaN thin film to form a thin film pair in which the InGaN thin filmand the GaN thin film are sequentially stacked, and the first step andthe second step may be alternately performed repeatedly a plurality oftimes.

In particular, the first step of forming the InGaN thin film may beperformed using MOCVD under nitrogen atmosphere (NH₃ or N₂). Also,hydrogen (H₂) may be supplied onto the upper portion of the InGaN thinfilm so that indium (In) included in the upper portion of the InGaN thinfilm is removed. In particular, the hydrogen (H₂) may be supplied ontothe upper portion of the InGaN thin film for about 25 seconds to about30 seconds at a speed of about 8,000 sccm to about 8,500 sccm.

FIG. 2 is a schematic diagram illustrating a method of manufacturing aninclined type superlattice thin film layer according to one embodimentof the present invention.

Referring to FIG. 2, trimethylgallium (TMG), trimethylindium (TMI) and anitrogen based gas (NH₃ or N₂) are supplied onto a substrate 100 onwhich the n-type semiconductor layer 200 is formed and which is disposedin an MOCVD apparatus to form an InGaN thin film. Then, hydrogen gas maybe supplied to the device, and indium (In) included in the upper portionof the InGaN thin film may be removed. In the embodiment of the presentinvention, the hydrogen (H₂) may be supplied for about 25 seconds toabout 30 seconds at a speed of about 8,000 sccm to about 8,500 sccm.Indium (In) included in the upper portion of the InGaN thin film isremoved, and thus InGaN thin film may become the GaN film. Thus, thethin film pair in which the InGaN thin film and the GaN thin film aresequentially stacked may be formed.

Since the above-described first step and the second step may bealternately performed repeatedly a plurality of times, the inclined typesuperlattice thin film layer 300 may have the structure including aplurality of thin film pairs in which the InGaN thin film and the GaNthin film are sequentially stacked. In the embodiment of the presentinvention, the inclined type superlattice thin film layer 300 may beformed by alternately performing each of the first step and second stepof forming the thin film pairs repeatedly two to twelve times. Thus, theinclined type superlattice thin film layer 300 may have a structure of 2to 100 pairs of the thin film pairs in which the InGaN thin films andthe GaN thin films sequentially stacked.

Also, after the first step and the second step are alternatelyperformed, the first step and the second step may be repeatedlyperformed at a temperature lower than that of the previously performedsteps. In particular, in the embodiment of the present invention, whenthe first step and the second step are repeatedly performed, the firststep and the second step may be performed at a temperature lower thanthe previously performed steps by 5° C.

Referring to FIG. 2, the first step and the second step may be firstlyperformed at about 925° C., and then, the first step and the second stepmay be secondly performed at a temperature lower than the temperature ofabout 925° C. Then, the first step and the second step may be thirdlyperformed at a temperature lower than the temperature of the secondperformance. By the above method, when the first step and the secondstep are alternately performed repeatedly, the first step and the secondstep may be performed at a temperature lower than the temperature of theprevious steps. As the temperature is lower, indium (In) composition isincreased, and thus as the number of repeated alternating performance ofthe first step and the second step is increased, an InGaN thin film inwhich the composition ration of indium (In) in the InGaN thin filmformed in the first step is increased may be formed. That is, thecomposition ratio of indium (In) of a second InGaN thin film formed bythe second performance may be greater than that of a first InGaN thinfilm formed by the first performance, and the composition ratio ofindium (In) of a third InGaN thin film formed by the third performancemay be greater than that of the second InGaN thin film.

As described above, when the plurality of thin film pairs in which InGaNthin films and GaN thin films of the embodiment of the present inventionare sequentially stacked are formed, by lowering the temperature of theperformance than that of the previous performance as the number ofperformances increases, the composition ratio of indium (In) included inthe InGaN thin film is increased as getting closer to the active layerto form the InGaN thin film, thereby forming the inclined typesuperlattice thin film layer having the sloped indium (In) concentrationgradient.

Referring to FIG. 1C, the method of manufacturing the light emittingdiode of the embodiment of the present invention may include 3) formingan active layer 400 having a quantum well structure on the inclined typesuperlattice thin film layer 300.

The active layer 400 of the quantum well structure is disposed betweenthe n-type semiconductor layer 200 and subsequent p-type semiconductorlayer 500 and is a light emitting layer configured to emit light due torecombination of injected electrons and holes. The active layer 400 mayhave a single quantum well structure or a multi quantum well (MQW)structure, and according to the embodiment of the present invention, theMQW structure may be applied. Generally, the active layer 400 of the MQWstructure represents a structure in which a barrier layer and a welllayer are alternately stacked, and the barrier layer has a bandgaphigher than that of the well layer, and thus, quantum confinement effectmay be effectively realized in the well layer. In the embodiment of thepresent invention, five well layers are used, but the present inventionis not limited by the above and more well layers may be used accordingto embodiments of the present invention.

When the light emitting diode is formed of a nitride-based compoundsemiconductor, the active layer 400 may be formed based on GaN. Inparticular, material having a bandgap lower than that of GaN isintroduced into the active layer 400, and a bandgap of the well layermay be adjusted. That is, the active layer 400 of the MQW structureincludes an InGaN layer of In_(x)Al_(y)Ga_((1-x-y))N(0≦x<1, 0≦y<1, and0≦x+y<1) as the well layer and a GaN layer as the barrier layer.

The formation of the active layer 400 on the inclined type superlatticethin film layer 300 may be performed through a conventionalmanufacturing method and for example, may be formed through MOCVDmethod, HVPE method, MBE method, e-beam deposition, sputtering, or thelike, but is not limited by the above.

Referring to FIG. 1D, the method of manufacturing the light emittingdiode of the embodiment of the present invention may include 4) forminga p-type semiconductor layer 500 on the active layer 400.

The p-type semiconductor layer 500 represents a semiconductor layerdoped with p-type dopants, and the p-type dopants may include any onematerial selected from magnesium (Mg), zinc (Zn), calcium (Ca),strontium (Sr), and barium (Ba). In particular, for example, the p-typesemiconductor layer 500 may include a nitride-based compoundsemiconductor including any one material selected from GaN orAl_(x)Ga_((1-x))N(0≦x<1). In the embodiment of the present invention,the p-type semiconductor layer 500 may include a p-GaN layer. Theformation of the p-type semiconductor layer 500 on the active layer 400may be performed through a conventional method, and the above-describedmethods of forming the n-type semiconductor layer 200 and the activelayer 400 may be used.

FIGS. 3A and 3B are schematic diagrams illustrating a method ofmanufacturing a light emitting diode according to another embodiment ofthe present invention.

Referring to FIG. 3A, before forming the active layer 400 of the quantumwell structure on the inclined type superlattice thin film layer 300, aGaN layer 350 may further be formed on the inclined type superlatticethin film layer 300. The GaN layer 350 may function as a cap layer toprevent damage of the inclined type superlattice thin film layer 300 bya process in which temperatures increase during the formation of theactive layer 400 on the inclined type superlattice thin film layer 300.The GaN layer 350 may be formed through the above-described method ofmanufacturing the semiconductor layer. Then, as shown in FIG. 3B, theactive layer 400 and the p-type semiconductor layer 500 may besequentially formed on the GaN layer 350.

As described above, the method of manufacturing the light emitting diodeof the embodiment of the present invention easily forms the inclinedtype superlattice thin film layer including the structure having theplurality of thin film pairs in which the InGaN thin films and the GaNthin films are alternately stacked by a temperature control and hydrogensupply, and thus, manufacturing efficiency of the high efficiency lightemitting diode having reduced residual strain and increased internalquantum efficiency may be improved. Also, the method of manufacturingthe light emitting diode of the embodiment of the present may beperformed using a conventional method of growing the light emittingdiode and equipment thereof, and thus, the above method may beeffectively used in related industries without additional cost. Inparticular, the growth temperature and the gas used in the process offorming the inclined type superlattice thin film layer of the embodimentof the present invention are similar to those for materials for thinfilms of a conventional light emitting diode, and thus, the technologymay have an excellent adaptability.

Light Emitting Diode Including Inclined Type Superlattice Thin FilmLayer

According to another aspect of the present invention, a light emittingdiode including an inclined type superlattice thin film layer may beprovided. The light emitting diode may be manufactured by theabove-described method of manufacturing the light emitting diodeincluding the inclined type superlattice thin film layer. In particular,the light emitting diode may include an n-type semiconductor layerdisposed on a substrate, an inclined type superlattice thin film layerdisposed on the n-type semiconductor layer and having a structureincluding a plurality of thin film pairs in which InGaN thin films andGaN thin films are sequentially stacked, an active layer having aquantum well structure disposed on the inclined type superlattice thinfilm layer, and a p-type semiconductor layer disposed on the activelayer. Here, the composition ratio of indium (In) included in the InGaNthin film of the inclined type superlattice thin film layer is increasedas getting closer to the active layer.

The light emitting diode is manufactured by the above-described methodof manufacturing the light emitting diode including the inclined typesuperlattice thin film layer, and thus, the light emitting diode may bethe same as described in the method of manufacturing the light emittingdiode including the inclined type superlattice thin film layer. Thus,the light emitting diode of the embodiment of the present invention isdescribed using the description of the method of manufacturing the lightemitting diode including the inclined type superlattice thin film layer,and thus, a detailed description will be omitted, and hereinafter,particular structures of the light emitting diode will be described.

FIGS. 4A and 4B are a schematic diagram illustrating a structure of alight emitting diode according to one embodiment of the presentinvention and an image of a light emitting diode manufactured accordingto Embodiment 1 observed using a transmission electron microscope (TEM).

Referring to FIG. 4A, the light emitting diode of the embodiment of thepresent invention includes an n-type semiconductor layer 200 on asubstrate 100, and an inclined type superlattice thin film layer 300including a plurality of thin film pairs in which InGaN thin films andGaN thin films are sequentially stacked on the n-type semiconductorlayer 200. An active layer 400 of a quantum well structure and a p-typesemiconductor layer 500 may be sequentially disposed on the inclinedtype superlattice thin film layer 300. The n-type semiconductor layer200 and the p-type semiconductor layer 500 may include an n-type GaNlayer and a p-type GaN layer, respectively.

FIG. 4B is a TEM image illustrating the structure of the light emittingdiode manufactured by Embodiment 1 of the present invention, and aninclined type superlattice thin film layer superbly formed in whichtwelve thin film pairs are stacked between the n-GaN layer and the multiquantum well structure can be seen.

In the embodiment of the present invention, the inclined typesuperlattice thin film layer 300 may have a structure in which thin filmpairs of 2 to 100 are disposed. Also, composition ratio of indium (In)included in the InGaN thin film is increased as getting closer to theactive layer.

As described above, the light emitting diode of the embodiment of thepresent invention includes the inclined type superlattice thin filmlayer 300 under the active layer 400, and band bending generated by thelattice mismatch in a quantum well structure of the active layer 400 maybe decreased. Thus, the light emitting diode of the embodiment of thepresent invention may reduce internal residual strain in the lightemitting diode and also reduce defects and enhance confinement effect ofcarriers, and thus, increasing internal quantum efficiency. Thus, as aresult, light output of the light emitting diode may be improved, andthe light emitting diode of the embodiment of the present invention maybe applied to all light emitting diodes, and in particular, when thelight emitting diode is applied to a green light emitting diode havingextremely low internal quantum efficiency, the effect may be increased.In particular, the above may be described by the following embodimentsand drawings in detail.

In the embodiment of the present invention, a GaN layer may further beformed between the inclined type superlattice thin film layer 300 andthe active layer 400. The GaN layer may function as a cap layer toprevent damage of the inclined type superlattice thin film layer 300.

Hereinafter, embodiments are described for an understanding of thepresent invention, but the following embodiments are only examples ofthe present invention, and the scope of the present invention will notbe limited by the following embodiments.

Embodiments Embodiment 1: Manufacturing Light Emitting Diode IncludingInclined Type Superlattice Thin Film Layer

An n-Gan layer was formed on a sapphire substrate using MOCVD apparatus.Then, at a temperature of 925° C., 100 sccm of trimethylgallium (TMG),270 sccm trimethylindium (TMI), and 28,000 sccm of ammonia gas (NH₃)were supplied to the apparatus for about 55 seconds to form an InGaNthin film of 2 nm thickness. Then, approximately 10% hydrogen gas in anitrogen gas atmosphere was flowed into the apparatus for about 25seconds at a speed of 8,400 sccm to remove indium included in an upperportion of the InGaN thin film. Then, indium included in the upperportion of about 0.8 nm to about 1.0 nm of the InGaN thin film formed ata thickness of about 2 nm was removed to form a GaN thin film. Formingthe above-described InGaN thin films and the GaN thin films werealternately performed 11 times to form an inclined type superlatticethin film layer having a thickness of 24 nm in which 12 thin film pairsincluding the InGaN thin films and the GaN thin films having a thicknessof 1 mm are disposed. During the 11 times repeated steps, a temperatureof the device, as shown in FIG. 2, was decreased by 5° C. per each step.Then, an active layer of a multi quantum well structure including fivequantum well layers and a p-GaN layer were sequentially formed on theinclined type superlattice thin film layer.

Comparative Embodiment 1: Light Emitting Diode Without Inclined TypeSuperlattice Thin Film Layer

A light emitting diode was manufactured in the same process as describedin Embodiment 1 except for forming the inclined type superlattice thinfilm layer.

Comparative Embodiment 2: Light Emitting Diode Including CART StructureLayer

A light emitting diode was manufactured in the same process as describedin Embodiment 1 except that a conventional CART structure layer wasformed instead of the inclined type superlattice thin film layer.

Generally, a conventional charge asymmetric resonance tunneling (CART)structure includes an InGaN layer of tens of nanometers which isinserted between an n-GaN layer and an active layer in order to increaseefficiency of a light emitting diode. Generally, indium composition ofan InGaN layer of the CART structure may be smaller than that of InGaNin the active layer (Characteristics and effect of the CART structureare described in “IEEE Trans. Elec. Dev. 49, 1093, (2002)”).

Comparative Embodiment 3: Light Emitting Diode Including SuperlatticeLayer

A light emitting diode was manufactured in the same process as describedin Embodiment 1 except that an n/p-[AlGaN/GaN] superlattice layer wasformed under the active layer using conventional Si and Mg dopingmaterials instead of the inclined type superlattice thin film layer wasformed (The method of manufacturing the superlattice layer is describedin “Light Emitting Diodes (LEDs) for Generating Illumination,” OIDATechnology Road Map Update 2002, 2002 and Manning Fan et al., “ColorFilter-less Technology of LED Back Light for LCD-TV,” Proc. SPIE, Vol.6841, 2007, pp. 68410G1-68410G6).

FIG. 5 is a table illustrating change of process temperature duringmanufacturing light emitting diodes according to Embodiment 1 andComparative Embodiments 1 to 3 of the present invention.

Referring to FIG. 5, different from Comparative Embodiment 1 toComparative Embodiment 3, in Embodiment 1 of the present invention, asthe number of repeated performance of the formation of the thin filmpairs in which InGaN thin films and GaN thin films of 2 nm aresequentially stacked is increased, a temperature of each step is smallerthan that of a previous step by about 5° C. This is for, as describedabove, increasing the composition ratio of indium (In) of the InGaN thinfilm included in the inclined type superlattice thin film layer asgetting closer to the active layer.

FIGS. 6A and 6B are tables describing photoluminescence intensity (PLintensity) according to a change of wavelength and temperature accordingto Embodiment 1 and Comparative Embodiments 1 to 3 of the presentinvention.

Referring to FIG. 6A, light excitation illumination intensity of thelight emitting diode of Embodiment 1 of the present invention isincreased by about 73.5% compared with Comparative Embodiment 1 toComparative Embodiment 3. Also, the peak position is blue-shifted byabout 2 nm to about 3 nm, and thus, the inclined type superlattice thinfilm layer of the present invention reduces a strain of the active layerand improves carrier injection efficiency.

Also, FIG. 6B is result of an IQE test, an analysis of defect density,and a measurement of activated energy based on data from low temperaturePL equipment at temperatures in a range of about 10K to 300K. This islow temperature PL data fitted using Arrhenius plots to show opticalcharacteristics of activation energy which contributes tonon-light-emitting energy and does not contribute to light emission, andthe increase of the IQE represents an improvement of the electron-holeoverlap wave function in an active layer. Thus, referring to FIG. 6B,the light emitting diode of Embodiment 1 of the present invention isimproved by 23.9% to 33.8% compared with Comparative Embodiments 1 toComparative Embodiment 3. Thus, when the light emitting diode accordingto embodiments of the present invention includes the inclined typesuperlattice thin film layer formed under the active layer, quantumconfinement effect is increased in the multiple quantum wells of theactive layer, the number of carriers that do not contribute to lightemission is decreased, and thus, non-light-emission caused by thedefects may be greatly decreased. Thus, internal quantum efficiency ofthe light emitting diode according to embodiments of the presentinvention may be improved.

FIGS. 7A and 7B are tables illustrating electrical characteristicsaccording to wavelength according to Embodiment 1 and ComparativeEmbodiments 1 to 3 of the present invention.

In particular, FIG. 7A represents measured output power of green LEDchips in which the light emitting diodes of Embodiment 1 and ComparativeEmbodiment 1 to Comparative Embodiment 3 are applied, using anintegrating sphere. In particular, the measurement values arerepresented by following Table 1.

TABLE 1 Primary Total Peak Lumi- Wave- Output Wave- nous Current Voltagelength Power length Flux Classification (mA) (V) (nm) (mW) (nm) (lm)Comparative 20 3.1 526 110 524 756 Embodiment 1 Comparative 20 3.1 525120 523 801 Embodiment 2 Comparative 20 3.3 524 143 523 879 Embodiment 3Embodiment 1 20 3.1 523 145 522 994

Referring to Table 1 and FIG. 7A, when current of 80 mA is applied,output intensity of the LED chip of Embodiment 1 of the presentinvention is greatly increased by 42.5% compared with ComparativeEmbodiment 1 to Comparative Embodiment 3. The above is because theinternal quantum efficiency is increased, thus may contribute toreducing the green gap effect.

Also, referring to FIG. 7B, resistance of the light emitting diode ofComparative Embodiment 1 is about 14.7Ω, and resistance of Embodiment 1of the present invention is about 9.9Ω, and thus, that the seriesresistance of the light emitting diode including the inclined typesuperlattice thin film layer according to embodiments of the presentinvention is greatly decreased can be confirmed. Also, turn-on voltageof the light emitting diode of the Embodiment 1 of the present inventionis reduced, and thus, that the current injection characteristic isimproved can be seen.

According to the embodiments of the present invention, the lightemitting diode includes an inclined type superlattice layer under theactive layer, and thus, internal residual strain may be reduced, andconfinement effect of carriers may be enhanced, thereby internal quantumefficiency may be improved.

Also, the inclined type superlattice thin film layer may be easilyformed through controlling temperature and supplying hydrogen withoutadditional process or equipment, and thus, efficiency of manufacturingthe high efficiency light emitting diode may be improved.

It will be apparent to those skilled in the art that variousmodifications can be made to the above-described embodiments of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention covers allsuch modifications provided they come within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A light emitting diode, comprising: an n-typesemiconductor layer disposed on a substrate; an inclined typesuperlattice thin film layer disposed on the n-type semiconductor layer,and including a plurality of thin film pairs in which InGaN thin filmsand GaN thin films are sequentially stacked; an active layer having aquantum well structure disposed on the inclined type superlattice thinfilm layer; and a p-type semiconductor layer disposed on the activelayer, wherein composition ratio of indium (In) included in the InGaNthin film is increased as getting closer to the active layer.
 2. Thelight emitting diode of claim 1, wherein the inclined type superlatticethin film layer has a structure in which the thin film pairs of 2 to 100are disposed.
 3. The light emitting diode of claim 1, wherein theinclined type superlattice thin film layer reduces band bendinggenerated by a lattice mismatch in the quantum well structure of theactive layer.
 4. The light emitting diode of claim 1, wherein the n-typesemiconductor layer and the p-type semiconductor layer comprise ann-type GaN layer and a p-type GaN layer, respectively.
 5. The lightemitting diode of claim 1, further comprising a GaN layer interposedbetween the inclined type superlattice thin film layer and the activelayer.
 6. A method of manufacturing a light emitting diode, comprising:forming an n-type semiconductor layer on a substrate; forming aninclined type superlattice thin film layer including a plurality of thinfilm pairs in which InGaN thin films and GaN thin films are sequentiallystacked on the n-type semiconductor layer; forming an active layerhaving a quantum well structure on the inclined type superlattice thinfilm layer; and forming a p-type semiconductor layer on the activelayer, wherein composition ratio of indium (In) included in the InGaNthin film is increased as getting closer to the active layer.
 7. Themethod of claim 6, wherein forming of the inclined type superlatticethin film layer comprises: a first step of forming the InGaN thin film;and a second step of removing indium included in an upper portion of theInGaN thin film to form the thin film pairs in which the InGaN thinfilms and the GaN thin films are sequentially stacked, wherein the firststep and the second step are alternately performed repeatedly aplurality of times.
 8. The method of claim 7, wherein the first step isperformed under nitrogen atmosphere using a metal organic chemical vapordeposition (MOCVD) method.
 9. The method of claim 7, wherein the secondstep comprises supplying hydrogen (H₂) on an upper portion of the InGaNthin film and removing indium (In) included in the upper portion of theInGaN thin film.
 10. The method of claim 9, wherein the hydrogen issupplied for 25 seconds to 30 seconds at a speed in a range of 8,000sccm to 8,500 sccm.
 11. The method of claim 7, wherein the inclined typesuperlattice thin film layer is formed by alternately performing thefirst step and the second step repeatedly 2 to 100 times.
 12. The methodof claim 7, wherein after the first step and the second step arealternately performed, the steps are performed at a temperature lowerthan the temperature of previous steps during repeatedly performing ofthe first step and the second step.
 13. The method of claim 12, whereinduring repeatedly performing of the first step and the second step, thesteps are performed at a temperature lower than the temperature ofprevious steps by 5° C.
 14. The method of claim 6, wherein beforeforming of the active layer of the quantum well structure on theinclined type superlattice thin film layer, further comprising forming aGaN layer on the inclined type superlattice thin film layer.